In lighting a room or workspace, it is important to have the light uniformly distributed. An incandescent bulb or a fluorescent tube, when illuminated, produces an area of high-intensity illumination bounded by areas of gradually decreasing intensity. When a person works under such a light, it tends to cause eyestrain due to the difference in the illumination and the glare from the bright spot immediately in line with the source of light.
In order to overcome this problem, it has been common practice in the past to put a diffuser in front of the incandescent bulb or fluorescent tube to spread the light over the workspace. While this improves the problem substantially, bright spots are still left which cause a problem in working and particularly in attempting read under such a light. The problem is particularly severe in attempting to read from a magazine or book printed on high gloss paper.
In 1981, Loren A. Whitehead obtained U.S. Pat. No. 4,260,220, Apr. 7, 1981, entitled PRISM LIGHT GUIDE HAVING SURFACES WHICH ARE IN OCTATURE. This patent was directed to a novel class of materials which could be used to pipe light into darkened areas. The material was a transparent sheet of plastic material having a smooth surface or a plano surface on one side and a pattern of elongated prism-like grooves on the opposite side. According to the teaching of the patent, the material could be formed into a hollow structure having a smooth inner surface and a grooved surface on the outside having the prisms or grooves running in the long direction of the structure. It was found, in using this material, that if light entered one end it would travel through the tube using total internal reflection to emerge at the far end without a substantial loss in brightness. Two additional patents were issued to Whitehead. The first, U.S. Pat. No. 4,542,449, on Sept. 17, 1985, and the second U.S. Pat. No. 4,615,579, Oct. 7, 1986, disclosed additional uses for the material. Again, the patents taught the use of the material as a light pipe and as a luminaire or source of light in which the material would be shaped and provided with extractors and reflecting surfaces to direct the light to emerge from one side of the elongated light pipe configuration.
Flat panels of the material are also taught using two sheets of material. The first sheet would be put in place with the prism surface pointing outward and a second sheet of the material would be laid over the first with the prism surface contacting the smooth surface of the first sheet and with the elongated prisms of the second sheet set at an angle to the prisms on the first sheet. The teaching of all three of these patents are incorporated herein by reference. The prismatic material is available in thin sheet from from the 3M Corporation where it is sold under the trademark SCOTCHLAMP. In all of the above-mentioned applications using the film, the light is imposed on the smooth surface and is conducted as a light pipe by internal reflections off of the prism faces or, in a luminaire or light panel configuration, the light strikes the smooth surface first and emerges from the corrugated or prism-like surface. No teaching is found in any of these patents for the use of the material with the corrugated or prism-like surface pointing inward toward the light source and with the smooth surface outward. Applicants have found some surprising and improved light diffusion effects when the film is used in this configuration.